U.S. patent number 10,359,391 [Application Number 15/204,371] was granted by the patent office on 2019-07-23 for sensor with a membrane having full circumferential adhesion.
This patent grant is currently assigned to e-SENS, Inc.. The grantee listed for this patent is e-SENS, Inc.. Invention is credited to Richard B. Brown, Ondrej Novak.
United States Patent |
10,359,391 |
Brown , et al. |
July 23, 2019 |
Sensor with a membrane having full circumferential adhesion
Abstract
Embodiments are directed to a chemical sensor and a method of
fabricating a chemical sensor that includes a membrane having full
circumferential adhesion. The chemical sensor device includes a
silicon substrate comprising a sensor-side and a backside. The
sensor-side includes a sensor-side electrode; a first passivation
layer disposed on the substrate; and a second passivation layer on
the first passivation layer and adjacent to the sensor-side
electrode, the passivation layer comprising an adhesion trench
exposing a portion of the first passivation layer, and a polyimide
ring disposed on the second passivation layer. The backside
includes a backside electrode on the backside of the substrate. The
substrate includes an electrically isolated doped region, such as a
through silicon via, electrically connecting the sensor-side
electrode and the backside electrode.
Inventors: |
Brown; Richard B. (Salt Lake
City, UT), Novak; Ondrej (North Salt Lake, UT) |
Applicant: |
Name |
City |
State |
Country |
Type |
e-SENS, Inc. |
Salt Lake City |
UT |
US |
|
|
Assignee: |
e-SENS, Inc. (Salt Lake City,
UT)
|
Family
ID: |
60910269 |
Appl.
No.: |
15/204,371 |
Filed: |
July 7, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20180011046 A1 |
Jan 11, 2018 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N
27/3335 (20130101) |
Current International
Class: |
G01N
27/333 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1353751 |
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Apr 2011 |
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EP |
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2001-147215 |
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May 2001 |
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JP |
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2002-131275 |
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May 2002 |
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JP |
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2008-191058 |
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Aug 2008 |
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JP |
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2003-0014527 |
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Feb 2003 |
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KR |
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WO 2002/058846 |
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Aug 2002 |
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WO |
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Other References
PCT International Search Report and Written Opinion in PCT
International Application U.S. Appl. No. PCT/US2017/041098 dated
Sep. 27, 2017. cited by applicant .
Franklin, Robert K. et al., "2.12 Chemical Sensors", The University
of Michigan Ann Arbor, MI, Sensicore, Inc., Ann Arbor, MI, The
University of Utah, Salt Lake City, UT, Elsevier B.V., 2008 (pp.
432-461) (29 pages). cited by applicant.
|
Primary Examiner: Schmiedel; Edward J.
Attorney, Agent or Firm: Alliance IP, LLC
Claims
What is claimed is:
1. A sensor device comprising: a silicon substrate comprising a
sensor-side and a backside, the backside on an opposite surface of
the silicon substrate from the sensor-side; the sensor-side
comprising: a sensor-side electrode; a first passivation layer
disposed on the silicon substrate; a second passivation layer on
the first passivation layer and adjacent to the sensor-side
electrode, the second passivation layer comprising an adhesion
trench exposing a portion of the first passivation layer, and a
polyimide ring disposed on the second passivation layer; the
backside comprising: a backside electrode on the backside of the
silicon substrate; and the silicon substrate comprising a
through-silicon via (TSV) electrically connecting the sensor-side
electrode and the backside electrode.
2. The sensor device of claim 1, wherein the first passivation
layer comprises silicon dioxide.
3. The sensor device of claim 1, wherein the second passivation
layer comprises one or both of silicon nitride or silicon
dioxide.
4. The sensor device of claim 1, wherein the sensor-side electrode
comprises silver chloride on silver.
5. The sensor device of claim 1, wherein the backside electrode
comprises gold.
6. The sensor device of claim 1, wherein the TSV comprises p-type
doped silicon insulated from the rest of the substrate.
7. The sensor device of claim 6, wherein the TSV is insulated from
the silicon substrate by a passivation layer between the p-type
doped silicon TSV and the silicon substrate.
8. The sensor device of claim 1, wherein the polyimide ring defines
a first diameter, and wherein the adhesion trench defines a second
diameter greater than the first diameter.
9. The sensor device of claim 1, further comprising a hydrogel
buffer solution disposed on the sensor-side electrode within the
polyimide ring.
10. The sensor device of claim 1, wherein the polyimide ring is a
first polyimide ring, the sensor device comprising a second
polyimide ring surrounding the adhesion trench and the first
polyimide ring.
11. The sensor device of claim 10, further comprising a polymeric
membrane covering the sensor-side electrode and the adhesion
trench, wherein the polymeric membrane is contained within the
second polyimide ring.
12. The sensor device of claim 11, wherein the polymeric membrane
comprises ionophores.
13. The sensor device of claim 11, wherein the polymeric membrane
comprises an ion selective membrane.
14. The sensor device of claim 11, wherein the polymeric membrane
contacts the first passivation layer within the adhesion
trench.
15. The sensor device of claim 11, further comprising an adhesion
layer disposed on the portion of the first passivation layer
exposed within the adhesion trench, wherein the polymeric membrane
is in contact with the adhesion layer.
16. A sensor device comprising: a substrate comprising a
sensor-side and a backside, the backside on an opposite surface of
the substrate from the sensor-side; the sensor-side comprising: a
sensor-side electrode; a first passivation layer disposed on the
substrate; and a second passivation layer on the first passivation
layer and adjacent to the sensor-side electrode, the second
passivation layer comprising an adhesion trench exposing a portion
of the first passivation layer, the backside comprising: a backside
electrode on the backside of the substrate; and the substrate
comprising a through-substrate via electrically connecting the
sensor-side electrode and the backside electrode.
17. The sensor device of claim 16, further comprising a ring
disposed on the second passivation layer, the ring comprising one
of SU-8 or polyimide.
18. The sensor device of claim 16, wherein the substrate comprises
one of silicon or glass or ceramic.
19. The sensor device of claim 17, wherein the ring defines a first
diameter, and wherein the adhesion trench defines a second diameter
greater than the first diameter.
20. The sensor device of claim 17, further comprising a hydrogel
buffer solution disposed on the sensor-side electrode within the
ring.
21. The sensor device of claim 17, wherein the ring is a first
ring, the sensor device comprising a second ring surrounding the
adhesion trench and the first ring.
22. The sensor device of claim 21, further comprising a polymeric
membrane covering the adhesion trench and contained within the
second ring.
Description
TECHNICAL FIELD
This disclosure pertains to membrane adhesion trenches, and more
particularly, to a chemical sensor with a membrane having full
circumferential adhesion to a substrate.
BACKGROUND
Chemical sensors can be fabricated using semiconductor technology.
The use of semiconductor manufacturing can result in a reduction of
size of the chemical sensor as well as mass fabrication of chemical
sensors, thereby reducing per unit cost of each sensor. More
generally, the use of semiconductor manufacturing to manufacture
sensors produces the same or similar benefits as it does for
electrical circuits: low cost per sensor, small size, and highly
reproducible behavior. Semiconductor manufacturing also facilitates
the integration of signal conditioning, compensation circuits and
actuators, i.e., entire sensing and control systems, which can
dramatically improve sensor performance for little increase in
cost.
Semiconductor manufacturing technology also provides precise
control of layer thickness and lateral dimensions, so that the
sensors can be miniaturized, and so that they will have
well-controlled characteristics. By making the sensors small, one
can calibrate them with small volumes of calibration solution.
Sample volumes can be small (which may not be important in testing
water, but may be important in testing other solutions, such as
blood samples from newborns). Operation of the sensors also
requires rinsing between samples, and storage in a controlled
solution. Volumes of all of these solutions can be smaller if the
sensors are miniaturized, as they are on the silicon
substrates.
SUMMARY
Chemical sensors, such as ion selective electrodes (ISEs), can be
made using ionophore-doped polymeric membranes. Polymeric membranes
do not adhere well to silicon nitride surfaces that are often used
to insulate silicon dies and to protect the silicon and other
conducting layers from the solution under test and from the
internal filling solution that is between the electrode and the
membrane. Silicon dioxide provides a higher level of adhesion for
the polymeric membranes than silicon nitride. Silicon dioxide,
however, absorbs water, making it a poor encapsulant for the
electronics. This disclosure describes the adhesion of a polymeric
membrane to the surface of a solid-state liquid chemical sensor,
thereby making the sensor more reliable and robust, and giving the
sensor a longer lifetime.
Aspects of the embodiments are directed to a sensor device. The
sensor device can be an ion selective chemical sensor. The sensor
device may include a substrate comprising a sensor-side and a
backside. The sensor-side can include a sensor-side electrode; a
first passivation layer disposed on the substrate; and a second
passivation layer on the first passivation layer and adjacent to
the sensor-side electrode, the second passivation layer comprising
an adhesion trench exposing a portion of the first passivation
layer. The backside may include a backside electrode on the
backside of the substrate. The substrate can include a
through-silicon via (TSV) electrically connecting the sensor-side
electrode and the backside electrode.
Aspects of the embodiments are directed to a sensor device. The
sensor device can be an ion selective chemical sensor. The sensor
device may include a substrate comprising a sensor-side and a
backside. The sensor side may include a sensor-side electrode; a
first passivation layer disposed on the substrate; and a second
passivation layer on the first passivation layer and adjacent to
the sensor-side electrode, the second passivation layer comprising
an adhesion trench exposing a portion of the first passivation
layer, and a polyimide ring disposed on the second passivation
layer. The backside may include a backside electrode on the
backside of the substrate. The substrate may include a
through-silicon via (TSV) electrically connecting the sensor-side
electrode and the backside electrode.
Aspects of the embodiments are directed to a method for forming a
sensor device. The method may include providing a silicon
substrate, the silicon substrate comprising an electrically
isolated doped region (electrically isolated from the substrate
with an SiO, the silicon substrate further comprising a front side
and a backside, the front side comprising a front side passivation
layer, and the backside comprising a backside passivation layer;
etching a portion of the backside passivation layer to expose a
portion of the electrically isolated doped region on the backside
of the silicon substrate; forming a backside electrode over the
electrically isolated doped region of the backside of the silicon
substrate; etching a portion of the front side passivation layer to
expose a portion of the electrically isolated doped region on the
front side of the silicon substrate; forming a front side electrode
on the portion of the electrically isolated doped region exposed on
the front side of the silicon substrate; forming a second
passivation layer on at least a portion of the front side first
passivation layer; etching a trench in the second passivation layer
around the sensor-side electrode to expose a portion of the front
side passivation layer; forming a first ring (e.g., an SU-8 or
polyimide or other material ring) between the trench and
sensor-side electrode; and forming a second ring (e.g., an SU-8 or
polyimide or other material ring) around the trench.
In some embodiments, the first passivation layer comprises silicon
dioxide.
In some embodiments, the second passivation layer comprises silicon
nitride and optionally, silicon dioxide.
In some embodiments, the sensor-side electrode comprises silver
chloride on silver.
In some embodiments, the backside electrode comprises gold.
In some embodiments, the TSV comprises p-type doped silicon
insulated from the rest of the substrate.
In some embodiments, the first ring defines a first diameter, and
wherein the adhesion trench defines a second diameter greater than
the first diameter.
Some embodiments may also include a hydrogel buffer solution
disposed on the sensor-side electrode within the polyimide
ring.
In some embodiments, the polyimide ring is a first polyimide ring,
the sensor device comprising a second polyimide ring surrounding
the adhesion trench and the first polyimide ring.
Some embodiments may also include a polymeric membrane covering the
adhesion trench and contained within the second polyimide ring.
In some embodiments, the polymeric membrane comprises
ionophores.
In some embodiments, the polymeric membrane comprises an ion
selective membrane.
In some embodiments, the polymeric membrane contacts the first
passivation layer within the adhesion trench.
Some embodiments may also include one or more adhesion layers
disposed on the portion of the first passivation layer exposed
within the adhesion trench, wherein the polymeric membrane is in
contact with the adhesion layer.
Some embodiments may also include forming a hydrogel internal
buffer on the front side electrode within the first polyimide
ring.
Some embodiments also include forming a polymeric membrane over the
sensor-side electrode, in the trench, and within the second
polyimide ring.
In some embodiments, forming the sensor-side electrode may also
include forming a platinum layer on the electrically isolated doped
region exposed on the front side of the silicon substrate; forming
a silver layer on the platinum layer; and forming a silver chloride
layer on the silver layer.
In some embodiments, the substrate comprises one of silicon or
glass or ceramic.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a sensor device in accordance with
embodiments of the present disclosure.
FIG. 2 is a schematic diagram of a sensor device that includes a
polymeric membrane in accordance with embodiments of the present
disclosure.
FIG. 3 is a schematic diagram of a top-down view of a sensor device
in accordance with embodiments of the present disclosure.
FIG. 4 is a schematic diagram of a chemical sensor with a membrane
having full circumferential adhesion to a substrate in accordance
with embodiments of the present disclosure.
FIGS. 5A-B are schematic diagrams of a process flow for forming a
backside electrode on the sensor device in accordance with
embodiments of the present disclosure.
FIGS. 6A-C are schematic diagrams of a process flow for forming a
chemical sensor with a membrane having full circumferential
adhesion to a substrate in accordance with embodiments of the
present disclosure.
DETAILED DESCRIPTION
Chemical sensors, such as ion selective electrodes (ISEs) can be
made using ionophore-doped polymeric membranes. For example, an ISE
can use an ion-selective polymeric membrane that contains the
ionophore Valinomycin for detecting potassium, or
4-tert-Butylcalix[4]arene-tetraacetic acid tetraethyl ester for
detecting sodium. The ionophore is a selective binding site for the
analyte. The polymeric membrane establishes a barrier between the
sensor electrode and an analyte solution. The polymeric membrane
facilitates the introduction of an analyte to the ionophore, which
binds the charged ion, creating a charge separation between the
interior of the polymeric membrane and the external aqueous
solution. The charge separation can be measured to determine the
presence of the specific analyte.
Polymeric membranes do not adhere well to silicon nitride surfaces
that are often used to insulate the silicon and to protect the
silicon and other conducting layers from the solutions under test
and from the internal filling solution that is between the
electrode and the membrane. Additionally, polymeric membranes
adhere better to silicon dioxide than to silicon nitride.
In this disclosure, a trench is formed in the protective silicon
nitride to expose the silicon dioxide passivation layer. The
trenches surround the entirety of the silver/silver chloride
electrode. The polymeric membrane can be deposited on the electrode
(or on the hydrogel buffer solution) to form a seamless membrane
attached to the adhesion ring around the entire electrode.
Electrical contact to the silver/silver chloride electrode is made
with a conductive via (e.g., a through-silicon via) through the
silicon substrate, from sensor-side to backside.
By using a backside electrode electrically coupled to the
silver/silver electrode through a via, the trench (also referred to
herein as an adhesion trench) can completely encircle the active
sensor, thereby minimizing areas in which there is poor adhesion of
the membrane to the surface. Polyimide, SU-8, or other
high-aspect-ratio photopolymers can be used to form structures
(e.g., polyimide rings) to "contain" the deposited membrane
cocktail (e.g., through surface tension).
FIG. 1 is a schematic diagram of a sensor device 100 in accordance
with embodiments of the present disclosure. The schematic diagram
shown in FIG. 1 is not drawn to scale, as a scaled illustration
would minimize device architecture. Sensor device 100 includes a
substrate 102. Substrate 102 can include silicon 104, such as
silicon <100>. The substrate 102 includes a "sensor-side" 101
and a "backside" 103. The sensor-side 101 can include a sensor-side
first passivation layer 106, which can be a silicon dioxide
(SiO.sub.2) layer 106. The substrate backside 103 can also include
a backside passivation layer 108, which can be silicon dioxide 108.
The term "layer" is used throughout this disclosure and is meant to
include one or more layers of a material, and is not limited to
meaning a monolayer or single atomic layer of a material.
The silicon substrate 102 can be doped to make it conductive, or
can include an electrically isolated doped region 110. The
electrically isolated doped region 110 can include a p-type dopant,
such as a boron p-type dopant. The sensor device 100 includes
sensor-side electrode 116 and a backside electrode 112. The
electrically isolated doped region 110 can electrically connect the
sensor-side electrode 116 with the backside electrode 112 and can
be electrically isolated from the rest of the substrate by a
passivation layer (e.g., SiO2 layer 109). This electrically
isolated doped region 110 can be referred to as a via 110.
The backside electrode 112 can include a conductive material, such
as a metal. In some embodiments, the backside electrode 112 may
include gold (Au). The backside electrode 112 can be accessed by a
bonding pad 114. In some embodiments, another backside passivation
layer 113 can be deposited over the backside electrode to protect
the backside 103 from damage. The backside passivation layer 113
can include silicon nitride or silicon dioxide.
The sensor-side 101 can include a sensor-side electrode 116. The
via 110 is physically and electrically connected to the sensor-side
electrode 116. The sensor-side electrode can include silver (Ag)
and silver chloride (AgCl). Silver chloride has a stable
interfacial potential to the internal filling solution and
desirable Ohmic properties.
In some embodiments, the via 110 is electrically and physically
connected to a thin platinum disc 118. The platinum disc 118 can be
completely covered by silver. The silver has a chloridized surface,
resulting in a silver/silver-chloride electrode.
On the sensor-side first passivation layer 106, is a sensor-side
second passivation layer 120. The sensor-side second passivation
layer 120 can include silicon nitride (Si.sub.3N.sub.4) and silicon
dioxide (SiO.sub.2). As an example, the sensor-side second
passivation layer 120 can be silicon nitride, or can include a
layer of silicon dioxide on top of silicon nitride.
In some embodiments, adjacent to the sensor-side electrode 116 is a
polyimide ring structure 126a residing on the sensor-side second
passivation layer 120. The polyimide ring 126a can be circular or
substantially circular, and surround the sensor-side electrode
116.
An adhesion trench 122a can be etched into the sensor-side second
passivation layer 120 adjacent to the polyimide ring structure
126a. The adhesion trench 122a can be a first adhesion trench 122a;
multiple adhesion trenches, such as the second adhesion trench 122b
can be formed adjacent to the first adhesion trench 122a. The first
and second adhesion trenches 122a and 122b can be circular or
substantially circular and can surround the sensor-side electrode
116 (and in some embodiments, surround the polyimide ring
126a).
The adhesion trenches 122a and 122b are etched to expose the
underlying sensor-side first passivation layer 106 (i.e., the
silicon dioxide 106). As mentioned above, polymeric membranes
demonstrate higher adhesion to the silicon dioxide 106 than they
would to the silicon nitride of the sensor-side second passivation
layer 120. The adhesion trenches 122a and 122b can thus facilitate
polymeric membrane adhesion to the sensor device 100. In some
embodiments, one or more adhesion promotion layers 124 can be added
to the silicon dioxide surface 106 to promote polymeric membrane
adhesion. The adhesion promotion layers 124 can include silane
(SiH4) or silanol. The shape of the adhesion trenches 122a and 122b
may also provide mechanical adhesion of the membrane to the
substrate.
In some embodiments, a second polyimide ring 126b can reside on the
sensor-side second passivation layer 120. The second polyimide ring
126b can be circular or substantially circular and can surround the
sensor-side electrode 116 and the adhesion trench 122a (and 122b or
others, if present).
Though described as a silicon substrate, substrate 102 could in
some embodiments be composed of glass or ceramic or other suitable
material.
FIG. 2 is a schematic diagram 200 of a sensor device 100 that
includes a polymeric membrane 202 in accordance with embodiments of
the present disclosure. The diagram 200 of FIG. 2 shows the sensor
device 100 of FIG. 1 with the addition of the polymeric membrane
202 as well as the hydrogel buffer solution 204. In FIG. 2, the
first polyimide ring 126a can be shown to define the size of the
hydrogel buffer solution 204. The outer polyimide ring 126b defines
the size of the polymeric membrane 202 that acts as the transducer
of the sensor device 100.
Also shown in FIG. 2 is the polymeric membrane 202 filling adhesion
trenches 122a and 122b, and adhering to the adhesion promotion
layer 124 on the silicon dioxide passivation layer 106. The
polymeric membrane 202 can be "confined" by the second polyimide
ring 126b based on the shape of the polyimide ring and based on
surface tension of the deposited polymeric membrane cocktail
solution, composed of the membrane components and organic
solvent.
The polymeric membrane 202 is shown to contact the hydrogel buffer
solution 204. The hydrogel buffer solution 204 can reside within
the first polyimide ring 126a and contact the electrode 116. The
hydrogel buffer solution 204 can stabilize the potential between
the polymeric membrane 202 and the electrode 116. To provide a
well-poised electrical contact to the polymeric membrane 202, a
hydrogel buffer solution 204 can be used between the silver/silver
chloride electrode 116 and the polymeric membrane 202. This
hydrogel-based filling solution 204 is buffered with high
concentrations of salts. The polymeric membrane 202 hydrates when
exposed to aqueous solutions, and the high salt content of the
hydrogel buffer solution 204 can generate considerable osmotic
pressure on the polymeric membrane 202 as water moves through the
membrane into the hydrogel.
The via 110 allows the polymeric membrane to seamlessly adhere to
the sensor device. The adhesion trench(es) 122a (and 122b) and the
resulting seamless adhesion of the polymeric membrane 202 to the
sensor device 100 prevents the osmotic pressure created by the
hydrogel buffer solution 204 from causing the hydrogel buffer
solution from leaking out from under the polymeric membrane 202 and
forming an electrical short circuit path around the membrane.
FIG. 3 is a schematic diagram 300 of a top-down sectional
illustration of a sensor device 100 in accordance with embodiments
of the present disclosure. The diagram 300 shows an illustration of
a top-down and sectional view of the sensor device 100. At the
center is the via 110. Above the via 110 is the platinum disk 118.
Above the platinum disk 118 is the silver/silver chloride electrode
116. Around the electrode 116 is the first polyimide ring 126a.
Adhesion trenches 122a and 122b surround the first polyimide ring
126a. The second polyimide ring 126b surrounds the adhesion
trenches 122a and 122b.
FIG. 4 is a schematic diagram 400 of a chemical sensor with a
membrane 402 having full circumferential adhesion to a substrate
404. The membrane 402 is shown to be in contact with the substrate
404, a portion of which is shown in FIG. 4. The membrane 402 covers
the various structures that form the chemical sensor 400, with the
exception of backside contacts and backside passivation layers
(i.e., the membrane covers all of the components of the chemical
sensor on the sensor-side of the substrate). For example, the
membrane 402 encloses a sensing area 406 that can include the
hydrogel internal filling solution, as well as the metal contact
layers described above. The membrane 402 also covers the SU-8 or
polyimide ring(s) (shown as rings 408 in FIG. 4). The membrane 402
also covers the adhesion trenches 410. Noteworthy is that FIG. 4
illustrates that the membrane 402 makes a full circumferential
adhesion to the first passivation layer.
FIGS. 5A-B are schematic diagrams 500 and 550 of a process flow for
forming a backside electrode on the sensor device in accordance
with embodiments of the present disclosure. Starting with FIG. 5A,
FIG. 5A is a schematic process flow diagram 500 showing a portion
of the process steps for forming a backside electrode. The starting
silicon substrate can include the sensor-side first passivation
layer of silicon dioxide, a backside passivation layer of silicon
dioxide, and an electrically isolated doped region that can serve
as a via (502). The electrically isolated doped region can be
electrically isolated from the rest of the substrate (which can
also be doped) by a passivation layer, such as an SiO2 layer). The
backside passivation layer can be etched using photolithographic
techniques to expose the via (504). A metal, such as gold, is
deposited on the backside of the sensor device and patterned using
photolithographic techniques to form an electrode (506) making an
electrical connection from the electrically isolated doped region
(via) to a bonding pad.
Turning to FIG. 5B, FIG. 5B is a schematic process diagram 550
showing a portion of the process steps for forming a backside
electrode. A protective passivation layer (for example silicon
dioxide or silicon nitride) can be formed on the backside of the
substrate to protect the backside and to protect the backside
electrode (508). The protective passivation layer can be etched to
reveal the metal backside electrode in a location offset from the
electrically isolated doped region to form an offset bonding pad
(510).
The through silicon via (TSV) (i.e., the electrically isolated
doped region between the sensor side of the substrate and the
backside of the substrate) can be isolated from the rest of the
substrate by a TSV passivation layer. This passivation layer can be
an SiO2 layer formed by forming an annular ring in the substrate
through etching techniques and oxidizing the resulting cavity
between the TSV and the substrate.
FIGS. 6A-C are schematic diagrams of a process flow for forming a
chemical sensor with a membrane having full circumferential
adhesion in accordance with embodiments of the present disclosure.
FIG. 6A is a schematic process flow diagram 600 for a first set of
process steps for forming a chemical sensor with a membrane having
full circumferential adhesion in accordance with embodiments of the
present disclosure. The sensor-side first passivation layer
(SiO.sub.2) can be etched using photolithographic techniques to
expose the core of the electrically isolated doped region (via)
(602). A platinum disk can be formed through photolithography and
deposition to cover the contact to the via (604). A sensor-side
second passivation layer can be deposited on the sensor side first
passivation layer (SiO.sub.2) and on the platinum disk (606). The
sensor-side second passivation layer can be silicon nitride and can
include a top layer of silicon dioxide.
FIG. 6B is a schematic process flow diagram 650 for a second set of
process steps for forming a chemical sensor with a membrane having
full circumferential adhesion in accordance with embodiments of the
present disclosure. The sensor-side second passivation layer can be
etched to expose the platinum disk. A metal, such as silver, can be
deposited on the platinum to create an electrical connection with
the via (608). The adhesion trench can be etched into the
sensor-side second passivation layer (e.g., using photolithographic
techniques) (610). One or more adhesion trenches can be etched. The
sensor-side second passivation layer is etched to expose the
underlying sensor-side first passivation layer (SiO.sub.2). In some
embodiments, an adhesion promoting material can be formed in the
trench to promote polymeric membrane adhesion to the surface of the
sensor device. The adhesion promoting material can include silane
or a silanol or other known adhesion promoting material.
FIG. 6C is a schematic process flow diagram 660 for a third set of
process steps for forming a chemical sensor with a membrane having
full circumferential adhesion in accordance with embodiments of the
present disclosure. High aspect-ratio photo polymer, such as
polyimide or SU-8 can be patterned into rings on the sensor-side
second passivation layer (612). The polymer rings can be formed by
techniques such as those described in U.S. Pat. No. 6,764,652,
filed Jan. 24, 2001 and U.S. Pat. No. 7,438,851, filed Apr. 30,
2004, the contents of which are incorporated by reference in its
entirety. A first polymer ring can be formed adjacent to the
electrode. A second polymer ring can be formed having a larger
diameter than the first polyimide ring.
The silver deposited on the platinum disk can undergo
chloridization to form the silver/silver chloride electrode (614).
Chloridization can be achieved by submerging the substrate in NaOCl
or other chloridizing solution. The result is a silver/silver
chloride electrode that can be used as the sensor-side electrode
for the sensor device.
Aspects described in this disclosure can employ thin-film
fabrication techniques to create the devices and structures
described herein, and to achieve advantages that are described
herein and that are readily apparent to those of skill in the
art.
Advantages of the present disclosure are readily apparent.
Advantages of using the through-silicon via to connect to the micro
ion-selective electrode may include the following:
Full circumference adhesion trenches can be cut through the silicon
nitride passivation layer to silicon dioxide, which has sites to
which the polymeric membrane can be covalently bonded. This
covalent bonding gives the polymeric membrane good adhesion to the
surface all the way around, preventing leakage paths between the
internal filling solution (hydrogel buffer solution) and the
solution under test, which would render the sensor unusable. The
use of an adhesion promoter can increase the adhesion by forming
stronger covalent bonds with the polymeric membrane.
In the current disclosure, the bonding pads for all of the sensor
connections (not just the ion-selective electrodes) can be on the
back side of the chip, which eliminates a major challenge of
building micro chemical sensors: insulating the bonding wires from
the test solution. In a conventional solid-state chemical sensor,
bond wires connect the chip to a printed circuit board, and all of
the conductors from the chip to the board and on the PCB must be
encapsulated so that they have extremely high impedance to the
solution under test.
The micro ISEs have very high impedance, so any leakage path can
push them out of equilibrium, causing errors. The micro
ion-selective electrodes (ISEs) are no longer subject to failure
due to pin-hole defects in the silicon nitride passivation layer,
because interconnect wires on the front side of the chip are
eliminated.
While certain embodiments have been described in detail, those
familiar with the art to which this disclosure relates will
recognize various additional and/or alternative designs,
embodiments, and process steps for making and using the sensor
device as described by the following claims.
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